Doubling the allowable height of condominium or apartment buildings that have a single staircase from three to six stories could give cities more housing options, a new report finds, especially on small lots where larger buildings don’t make sense.
Though the analysis by Harvard University’s Joint Center for Housing Studies focuses on homes in the Boston area, the issue applies in much of the U.S. because most states adopt the same building rules. The International Building Code requires any residential structure with more than three stories to have at least two staircases to maximize fire safety. Ironically given the code’s name, most countries in Europe, Asia and South America do not use this standard and allow buildings up to at least six stories with a single set of stairs.
A number of U.S. states are studying whether to loosen their restrictions on taller single-staircase residential buildings, while firefighting advocacy groups such as the International Association of Fire Fighters have strongly opposed these changes.
Requiring two staircases raises developers’ costs significantly while limiting their options as they design buildings, according to the findings released in October. It has led to the dominance in many U.S. cities of so-called five-over-one multifamily buildings that feature five wood-framed floors over a ground-level concrete podium. These buildings often extend far down a city block to make room for the extra staircase while still maximizing the number of housing units. Developers typically don’t want to build taller because building codes would require them to use more costly steel and concrete.
Mid-rise apartment buildings of up to six stories on narrow lots have a potentially important role to play in meeting the affordable housing challenge in U.S. cities, the Joint Center said. One particular benefit would be to enable developers to provide more large units with three or more bedrooms suitable for families, according to the report.
In the typical five-over-one building in the Boston area, just 5% of the apartments have three or more bedrooms, with studios, one- and two-bedroom units making up the rest. That’s because building codes require each bedroom to have windows and the design of these larger multifamily buildings means many units have significant space facing internal hallways.
“The proposal to expand single-stair buildings would allow missing middle housing that has the potential to be more affordable,” said Chris Herbert, the Joint Center’s director, during an event where the report was made public. “It does also raise legitimate questions about safety.”
Safety issues
A central argument for requiring two staircases is that when there is only one, access can be compromised during an emergency. Building occupants may be trying to evacuate a structure in the same stairwell firefighters are using, for example.
“History is filled with examples of incidents where a single means of egress and blocked egress resulted in trapped occupants and loss of life,” the IAFF said in a joint statement in June with the Metropolitan Fire Chiefs Association.
The Joint Center report found that improvements in fire protection over the past century have made buildings much safer, including those that have wood framing. Technologies that help include automatic door closers, sprinkler systems and the use of nonflammable building materials.
Seattle, New York City and Honolulu are the only major U.S. cities that deviate from the international building code standard of requiring two staircases beyond three stories, according to the report. However, legislators in California, Oregon and Washington recently approved measures to move toward allowing taller buildings with one staircase statewide, and other states are considering similar changes.
Seattle legalized single-stair buildings up to six stories in the 1970s. The city's building code requires stairwells to have sprinklers and to withstand fire damage for two hours, according to a report by the National Fire Protection Association. The report says that some cities may lack such stringent protections or the type of equipment, such as long ladders, needed to reach the top of a six-story building.
Jansen Court Apartments in Seattle’s Capitol Hill neighborhood is an example of what is possible to build on a small lot with more lenient height restrictions. The 4.5-story property features two sets of five units with an exterior stairwell in the middle. The building, designed by Seattle-based Cast Architecture in 2019, was constructed on the back side of a 3,000-square-foot lot that already had a house in front.
“It really illustrates the upside of being able to design with one stair, because the project wouldn’t exist if I had to add another,” said Matt Hutchins, a principal at Cast Architecture in Seattle, in an interview about Jansen Court.
New York City has built more than 4,000 single-staircase buildings of four to six stories in the past six decades, said Stephen Smith, executive director of the Center for Building in North America, in an email. These don’t include structures with exterior staircases, a common feature in older buildings in New York. Smith’s group supports loosening the rules that govern stairwells in apartment buildings.
Smith told the NFPA at a meeting in September that the available data for New York since 2012 shows no evidence that any deaths in fatal fires could be attributed to living in a building with a single set of stairs. Most of the 4,000 buildings were constructed after 1999, he said, when sprinklers were required.
The Joint Center report was coauthored by architectural firm Utile and Boston Indicators, the research arm of The Boston Foundation.